he doesn't want to lose out on interest on that money. It's not a matter of planning ahead, it's a matter of keeping the money for as long as possible. Getting a refund is the worst possible scenario, because that means that the government got a free loan from you.

Did them early, owe again, reasonable number that I plan for every year, filing just enough on quarterly payments to make sure there is no penalty, wrote the checks, sealed the envelopes, and they are waiting for April 15th when they go into the post office... no reason to pay earlier than required.